This invention relates to piston-type injection pumps adapted to supply fuel for internal combustion engines, for example, diesel engines. A discharge valve generally is mounted in a sleeve between the working space of the pump and a discharge conduit. The latter conduit has a variable expansion space, the maximum volume of which is smaller than the space delimited by the lower face of the discharge valve member and by a gasket in the extreme position of the discharge valve member most distant from the working space of the pump.
Injection pumps of this type having a discharge valve are already known. Such injection pumps have a prestressed spring which acts on the valve member. At the start of an actuating stroke by the pump piston, when the pump piston is beginning its guided motion, the prestress of a spring acting on the valve member is equal to zero and in the course of the pressure stroke the valve member is entrained due to the overpressure of fuel expanding from the discharge conduit of the injection pump, whereby the valve member does not come in contact with its seat even at the highest rotating speed and with the largest fuel doses. A drawback of such arrangements is the relatively high maintenance requirements; in addition, the spring is unduly long and becomes shorter after long periods of operation and, as a result, causes malfunctioning in the operation of such a valve. Such a spring also requires a certain space above the valve proper, which forms a dead space. The stroke of the valve member in the course of fuel discharge increases for higher revolutions of the injection pump causing undesirable inaccuracies in its operation.